1. Field of the Invention
The present invention is directed to a diagnostic magnetic resonance apparatus, and in particular to an apparatus of the type having an examination part in which a patient is at least partially surrounded by a housing, and a freely movable reception antenna for receiving high-frequency magnetic resonance signals during an examination, the reception antenna having a pluggable, flexible cable connected thereto by means of which the antenna forwards the received magnetic resonance signals to processing circuitry.
2. Description of the Prior Art
In diagnostic magnetic resonance systems (NMR systems), specific reception antennas are used in addition whole body antennas for receiving the high-frequency magnetic resonance signals which arise during the course of an examination. The signals are processed by processing circuitry in order to generate a tomogram of regions of the human body such as, for example, tomograms of the knee, the head, or the eye. Such reception antennas are also known as local antennas or surface antennas. Local antennas offer a better signal-to-noise ratio compared to whole body antennas. Local antennas are often freely movable, and are connected to the processing circuitry contained in the examination apparatus via a flexible cable.
In known systems, the connecting cable is rigidly connected to the local antenna, and is provided with a plug-type unit at its opposite end, by means of which the user can connect the local antenna to a reception channel inside the housing of the examination part.
The term "rigidly connected" as used herein means that the connecting cable cannot be separated from the local antenna in the course of normal use. A pre-amplifier for amplifying the nuclear magnetic resonance signals is arranged in this known system in the housing of the examination part itself, immediately following the plug-type device. This arrangement has the advantage of providing only one pre-amplifier which can be used for the connection of all of the various local antennas, however, the signal-to-noise ratio is degraded by the attenuation of the intervening cables and conductor sections.
In another known solution, which is more complicated, a pre-amplifier is built into the housing of each local antenna. Again, the connecting cable is rigidly connected to the local antenna, and has a plug-type unit at the opposite end. Compared to the former arrangement, in the latter arrangement the signal-to-noise ratio is increased only by the noise factor of the pre-amplifier, due to the absence of intervening connecting lines.